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Genetic technology and agriculture
Genetic technology and agriculture
Genetically modified plants.
Proteins for use in medicine can be produced from genetically modified plants, so avoiding any problem of contamination by animal proteins. Examples include vaccines, albumin and the proteins found in breast milk that are used to treat diarrhoea in infants. However, the vast bulk of genetically modified plants grown around the world are crop plants modified to be resistant to herbicides, such as glufosinate and glyphosate, or crops that are resistant to insect pests. These modifications increase crop yield. A few crops, such as vitamin A-enhanced rice, provide improved nutrition.
Herbicide Resistant Crops
Herbicide Resistant Crops
Oil seed rape, Brassica napus, is grown in many parts of the world as a source of vegetable oil which is used as biodiesel fuel, as a lubricant and in human and animal foods (Figure 19.20). Natural rape seed oil contains substances (erucic acid and glucosinolates) that are undesirable in oil that is to be used in human or animal food. A hybrid, bred in Canada to produce low concentrations of these undesirable substances, was called canola (Canadian oilseed low acid), and this name is now often used to mean any variety of oil seed rape.
Gene technology has been used to produce herbicideresistant strains. Growing a herbicide-resistant crop allows fields to be sprayed with herbicide after the crop has germinated, killing any weeds that would otherwise compete with the crop for space, light, water or ions. This increases the yield of the crop. Oil seed rape that is resistant to the herbicide glyphosate, or to the related glufosinate, is grown in a number of countries.
Glyphosate inhibits an enzyme involved in the synthesis of three amino acids: phenylalanine, tyrosine and tryptophan. Glyphosate is absorbed by a plant’s leaves and is transported to the growing tips. The amino acids are needed for producing essential proteins, so the plant dies. Various microorganisms have versions of the enzyme involved in the synthesis of phenylalanine, tyrosine and tryptophan that are not affected by glyphosate. The gene that was transferred into crop plants came from a strain of the bacterium Agrobacterium.
Tobacco has been made resistant to two different herbicides: sulfonylurea and dinitroaniline. In both cases the genes were taken from other species of plant.
The most likely detrimental effects on the environment of growing a herbicide-resistant crop are that:
The most likely detrimental effects on the environment of growing a herbicide-resistant crop are that:
- the genetically modified plant will become an agricultural weed
- pollen will transfer the gene to wild relatives, producing hybrid offspring that are invasive weeds
- herbicide-resistant weeds will evolve because so much of the same herbicide is used.
The genetically modified plant will become an agricultural weed
The genetically modified plant will become an agricultural weed
In 1993, an investigation to compare invasiveness of normal and genetically modified oil seed rape plants was carried out. Three genetic lines were compared: nonengineered oilseed rape and two different genetically engineered versions of the same cultivar. The rates of population increase were compared in plants grown in a total of 12 different environments. The environments differed in, for example, the presence and absence of cultivated and uncultivated background vegetation, and presence and absence of various herbivores and pathogens. There was no evidence that genetic engineering increased the invasiveness of oil seed rape plants. Where differences between normal and genetically modified plants existed, the genetically engineered plants were slightly less invasive than the unmodified plants.
Pollen will transfer the gene to wild relatives, producing hybrid offspring that are invasive weeds
Pollen will transfer the gene to wild relatives, producing hybrid offspring that are invasive weeds
The risk of pollen transfer, by wind or by insects, is real. Oil seed rape interbreeds easily with two related species: wild radish and wild turnip. Its flowers are adapted for insect pollination, but are also pollinated by wind. Although ‘safe’ planting distances are specified for trials of genetically modified plants (for example, 200 m for oil seed rape), pollen from various plants has been found between 1000 and 1500 m away from those plants. Bees visiting some flowers have been found to forage at distances of more than 4000 m. Safe planting distances should be increased to allow the organic farming industry to maintain its ‘GM-free’ certification.
Herbicide-resistant weeds will evolve because so much of the same herbicide is used.
Herbicide-resistant mutant plants of various species have been found growing near fields where glyphosate has been much used. However, the herbicide is not only used on resistant crop species. Gene technology is not directly responsible for this evolution of resistance, which may arise in the absence of any genetically modified crop.
Insect Resistant Crops
Insect Resistant Crops
Another important agricultural development is that of genetically modified plants protected against attack by insect pests. Maize is protected against the corn borer, which eats the leaves of the plants and then burrows into the stalk, eating its way upwards until the plant cannot support the ear. Cotton is protected against pests such as the boll weevil (Figure 19.21). In both plants, yield is improved. Insect-resistant tobacco also exists, and is protected against the tobacco bud worm, but as yet it has not been grown commercially.
The most likely detrimental effects on the environment of growing an insect-resistant crop are:
- the evolution of resistance by the insect pests
- a damaging effect on other species of insects
- the transfer of the added gene to other species of plant.
However, less pesticide is used, reducing the risk of spray carrying to and affecting non-target species of insects in other areas. Remember also that only insects that actually eat the crop are affected.
A gene for a toxin, Bt toxin, which is lethal to insects that eat it but harmless to other animals, has been taken from a bacterium, Bacillus thuringiensis. Different strains of B. thuringiensis produce different toxins that can be used against different insect species. Crop plants that contain the Bt toxin gene from B. thuringiensis produce their own insecticides. However, insect populations can evolve resistance to toxins. Large numbers of crop plants containing the genes for Bt toxin may accelerate the evolution of resistance to it. Many populations of corn borers in the USA are now resistant to Bt toxin. From the outset, growers have been encouraged to plant up to 50% of their maize as non-genetically modified maize in so called ‘refuges’. Bt resistance in corn borers happens to be a recessive allele. Adult corn borers in the refuges are mostly homozygous dominant or heterozygous. These insects supply the dominant alleles to counteract resistance when adult corn borers from fields and refuges mate.
The pollen of Bt maize (corn) expresses the gene and has been found to disperse at least 60 m by wind. In the USA, milkweed frequently grows around the edge of maize fields and is a food source for the caterpillars of the monarch butterfly. Half of the summer population of monarch butterflies is found in the maize-growing areas of the USA. An experiment was set up in which caterpillars were fed milkweed leaves dusted with pollen from Bt maize, pollen from unmodified maize or no pollen at all. Caterpillar survival after four days of feeding on leaves dusted with pollen from Bt maize was 56%, whereas no caterpillars died after eating leaves dusted with pollen from unmodified maize or leaves with no pollen. However, further studies have shown that this laboratory-based experiment does not reflect the situation in the field, where the butterflies and caterpillars are not normally present at the time when pollen is shed.
Various aquatic insect larvae live in the streams in the maize-growing areas of the USA. Leaves from genetically modified Bt plants end up in the streams and may be eaten by, for example, caddis larvae. Experiments showed a small reduction in growth of larvae fed on Bt leaves. Another experiment, in which caddis larvae were fed on material containing different concentrations of Bt toxin, found a significant effect on larval growth at a concentration twice that actually found in the streams. This is, as yet, a potential rather than an actual problem, but one that needs careful monitoring.
It must not be forgotten that genetically modified crop seed is expensive and that its cost may remove any advantage of growing resistant crops. Growers need to buy seed each season, which again keeps costs high when compared with those of traditional varieties. In parts of the world where a great deal of a genetically modified crop is grown, there is the danger of losing biodiversity
Golden Rice
Golden Rice
Rice is a staple food in many parts of the world. Where people are poor and rice forms the major part of their diet, deficiency of vitamin A is a common and serious problem. Vitamin A deficiency can cause blindness. The World Health Organization estimates that as many as 800 000 children go blind each year as a result of vitamin A deficiency. Even more importantly, lack of vitamin A can cause an immune deficiency syndrome, and this is a significant cause of mortality in some parts of the world, particularly in children. It is estimated that, in 2010, more than two and half million children died of vitamin A deficiency.
From the WHO
The available evidence suggests that nearly 800000 deaths worldwide can be attributed to vitamin A deficiency among women and children. Approximately 20–24% of child mortality from measles, diarrhoea and malaria and 20% of all-cause maternal mortality can be attributed to this preventable condition. Africa and South-East Asia have the highest burden of disease.
Vitamin A is a fat-soluble vitamin found in oily fish and animal products such as eggs, milk, cheese and liver. It is also made in our bodies from carotene, the orange carotenoid pigment found in carrots. Pro-vitamin A carotenoids are also present in the aleurone layer of rice grains, but not in the endosperm, the energy storage tissue in the seed that humans eat. The aleurone layer is removed from rice when it is polished to produce white rice. Brown rice still contains the aleurone layer. The aleurone layer goes rancid if the rice is stored for any length of time, which is why white rice is produced and usually eaten instead. Children of families living in poverty often lack animal products in their diets as they are too expensive. Even if such children have a diet containing a wide range of vegetables rich in carotenoids, it is still difficult for them to avoid vitamin A deficiency.
Brown Rice and White Rice
Using Biotechnology to create Golden Rice
Using Biotechnology to create Golden Rice
In the 1990s, a project was undertaken to produce a variety of rice that contained carotene in its endosperm. Genes for carotene production were taken from daffodils and a common soil bacterium, now named Pantoea ananatis, and inserted into rice. Further research showed that substituting the gene from daffodil with one from maize gave even higher quantities of carotene, and the single transformation with these genes is the basis of all current Golden Rice. The genetically modified rice is called Golden Rice, because it contains a lot of the orange pigment carotene
The genetically modified rice is being bred into other varieties of rice to produce varieties that grow well in the conditions in different parts of the world, with the same yield, pest resistance and eating qualities as the original varieties. For example, the International Rice Research Institute (IRRI) has worked with researchers in Bangladesh to produce a pro-vitamin A enhanced ('Golden') variety of Bangladesh’s most popular rice variety. Research with children in China has shown that Golden Rice may be as useful as a source of vitamin A from vitamin A capsules, eggs, or milk to overcome vitamin A deficiency in rice-consuming populations.
There has been quite a lot of controversy over Golden Rice. Several non-governmental organisations, opposed to the use of genetic engineering in any crops, have condemned Golden Rice as being the wrong way to solve the problem of people eating diets that are short of vitamin A. One of their arguments is that the main reason that people eat diets that are short of vitamin A is poverty, and that the way to solve the problem is to help them out of poverty so that they have access to a more varied diet. Others say that, although it would be better if we could somehow lift these people out of poverty, this cannot be quickly achieved.
Despite the research, development and evaluation of Golden Rice that has taken place over the last ten years, it is not yet available to farmers and consumers because it has to be approved by national authorities in each country first.
With the help of the scientists who initially donated their technology invention, an international network of public sector rice research institutes and funding from bodies such as the Bill and Melinda Gates Foundation, Golden Rice seed will made available in developing countries at no greater cost than white rice seed. Everyone agrees that we need to solve the root causes of poor diets – which include numerous political, cultural and economic issues – but, meanwhile, pro-vitamin A enhanced rice could help millions of people to avoid blindness or death.
Genetically Modified Animals
Genetically Modified Animals
Genetically modified animals for food production are much rarer than crop plants. An example is the GM Atlantic salmon, developed in the USA and Canada (Figure 19.24). A growth-hormone regulating gene from a Pacific Chinook salmon and a promoter from another species of fish, an ocean pout, were injected into a fertilised egg of an Atlantic salmon. By producing growth hormone throughout the year, the salmon are able to grow all year, instead of just in spring and summer. As a result, fish reach market size in about eighteen months, compared with the three years needed by an unmodified fish. It is proposed to rear only sterile females and to farm them in land-based tanks. The characteristics of the GM salmon reduce their ability to compete with wild salmon in a natural environment. This has led the US Food and Drug Administration (FDA) to declare that they are ʻhighly unlikely to have any significant effects on the environmentʼ and ʻas safe as food as conventional Atlantic salmonʼ. In 2013, Canada approved the production of GM salmon eggs on a commercial scale, but neither Canada nor the USA FDA had yet given permission for GM salmon to enter the human food chain.
Social implications of using genetically modified organisms in food production
Social implications of using genetically modified organisms in food production
Some genetically modified plants are grown in strict containment in glasshouses, but a totally different set of problems emerges when genetically engineered organisms such as crop plants and organisms for the biologicalcontrol of pests are intended for use in the general environment. Can such organisms be used safely? It might seem likely that few countries would object to the growth of genetically modified crops that produce vaccines for human or animal use, yet there are people who object to the growth of pro-vitamin A enhanced rice (page 482). However, most objections are raised against the growth of herbicide-resistant or insect-resistant crops. The concerns about these genetically modified crops are as follows.
- The modified crop plants may become agricultural weeds or invade natural habitats.
- The introduced gene(s) may be transferred by pollen to wild relatives whose hybrid offspring may become more invasive.
- The introduced gene(s) may be transferred by pollen to unmodified plants growing on a farm with organic certification.
- The modified plants may be a direct hazard to humans, domestic animals or other beneficial animals, by being toxic or producing allergies.
- The herbicide that can now be used on the crop will leave toxic residues in the crop.
- Genetically modified seeds are expensive, as is herbicide, and their cost may remove any advantage of growing a resistant crop.
- Growers mostly need to buy seed each season, keeping costs high, unlike for traditional varieties, where the grower kept seed from one crop to sow for the next.
- In parts of the world where a lot of genetically modified crops are grown, there is a danger of losing traditional varieties with their desirable background genes for particular localities and their possibly unknown traits that might be useful in a world where the climate is changing. This requires a programme of growing and harvesting traditional varieties and setting up a seed bank to preserve them.
It is a long-term seed storage facility, built to stand the test of time — and the challenge of natural or man-made disasters. The Seed Vault represents the world’s largest collection of crop diversity.
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